1. Field of the Invention
This invention generally relates to an internal hub transmission for a bicycle. More specifically, the present invention relates to an internal hub transmission which uses a sealing assembly that rotates with the hub shell.
2. Background Information
Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle. Some bicycles are equipped with a transmission for making riding up and down hills easier. One type of bicycle transmission component is an internal hub transmission. The internal hub transmission has been extensively redesigned over the years.
Bicycles, particularly recreational bicycles referred to as city cruisers, are inexpensive and are easy to ride, and are thus widely used to commute to work or school or for shopping. With this type of recreational bicycle, an internal hub transmission is sometimes mounted at the rear wheel in order to ride at high speeds over flat terrain or to ride uphill with minimal exertion.
An internal hub transmission generally comprises a hub axle that is fixed to the bicycle frame; a hub shell that is able to rotate around the hub axle; a driving member for receiving a driving force from the drive chain; a planet gear mechanism that is housed in the hub shell for transmitting the driving force from the driving member to the hub shell through a plurality of transmission paths; and a clutch mechanism for selecting among the plurality of transmission paths. The clutch mechanism has a clutch member for switching the drive transmission path by moving in the direction of the hub axis, and a push rod that presses the clutch member.
Because the driving member and hub shell are capable of rotation relative to each other, there is a space between the two which creates a risk that water, dirt and other contaminants may enter the inside of the hub shell and adversely affect the operation of the planet gear mechanism and other components. Some internal hub transmissions use a labyrinth-type sealing mechanism to inhibit entry of contaminants into the hub shell. However, since such a system relies on staggered barrier walls with spaces between the barrier walls, there is still a risk that contaminants can migrate between the barrier walls and enter the inside of the hub shell, especially if the hub is immersed in water. Other internal transmission hubs use a rubber seal mounted to an inner peripheral surface of an annular metal ring, which, in turn, is press-fit onto the inner peripheral surface of the hub shell. While such a sealing mechanism is effective, the rubber seal inevitably becomes worn as a result of the sliding contact with the driving member as the hub rotates relative to the driving member. Because the annular ring containing the rubber seal is press-fit onto the inner peripheral surface of the hub shell, removal of the old seal and installation of a new seal is very difficult. Finally, there are covers for a bicycle transmission including an annular housing and an annular seal member, wherein the housing includes a side wall that defines a plurality of circumferentially disposed slots, and the seal member is retained within the housing and extends radially inwardly, and wherein the seal member is formed from a resilient material, and the housing is formed from a material that is more rigid than the seal member. Such an arrangement allows easy removal and replacement of the cover, and can for example be taken from European Patent Application No. 1040993.
Experience has shown, however, that even with the latter mentioned type of seal for a bicycle hub transmission, entry of contaminants into the hub can only be prevented in part, with dust particles still able to make their way through the various interfaces between the seal and the relevant parts of the hub transmission. Accordingly, there is a need for further enhancement of this type of seal to obtain a more reliable and effective sealing of the hub transmission from contaminants. In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved internal hub transmission. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.